The present invention relates generally to packet based video broadcast systems. More particularly, the present invention pertains to methods of estimating the extent of loss of video coding layer information and their impact in a series of images in an encrypted video stream that uses MPEG2/4/H.264-AVC compatible encoding.
In typical broadcast systems, such as in IPTV (Internet Protocol Television) and direct broadcast satellite (DBS) applications, multiple video programs are encoded in parallel, and the digitally compressed bitstreams are multiplexed onto a single, constant or variable bit rate channel. The video coding layer (MPEG2/H.264-AVC) is typically packetized into small fixed-size packets (MPEG2 Transport Stream) before transmission to an IP network. Typical packet losses in an IP network could follow various loss distributions where each loss event could be single, consecutive or sparse burst losses. This loss will result in a discard of a frame, slice or macroblock/s at the video coding layer. These macroblocks could either be INTER or INTRA predicted and could be part of the reference frame list, in which case the temporal duration of the loss could extend for a few frames in sequence.
Just measuring the packet loss rate at the IP level is insufficient to determine the loss propagation at the video content layer. The visual impact of IP packet loss must be determined by analyzing the loss propagation at the video content layer. In addition, coding quality is largely dependent on the quantization errors, the distribution of quantization at each macroblock determines the coding quality, the higher the quantization, the higher the loss of DCT coefficients, that results in low image quality. In an encrypted environment all the information that is needed to determine the spatial and temporal extent of the propagation of errors and quantization data is unavailable. Typically, the transport stream payload is encrypted. This payload contains the information about the video coding layer information at various sections, frames, slices and macroblocks. What is needed is a method to determine this information when the video stream monitored by the measurement device is encrypted.
MPEG encoded variable bit rate (VBR) video traffic is expected to dominate the bandwidth of broadband networks. Such traffic can be delivered in streaming, on demand, IPTV or DBS types of environments. Accurate models must take into account both capped VBR or CBR types of environment, video complexity and spatial/temporal propagation of errors under various loss distribution patterns. These parameters are necessary to enable monitoring systems for prediction of performance of any proposed network during its operation. FIG. 1 shows components that are involved in delivering video content in a typical IPTV environment. Video source that originates as analog signal is encoded using an encoder and packetized and sent using an IP network. It could be sent as multicast or unicast destination to the network. The core contains various elements to provision and manage subscribers and traffic flows. The content is stored in content servers and delivered to the user on demand.
MPEG coding standards define timing information at various sections in a video that is used by the Video decoding process. FIG. 2 shows the packet layers where this timing information is present. There is a single, common system clock in the encoder. This clock is used to create timestamps that indicate the correct presentation and decoding timing of audio and video, as well as to create timestamps that indicate the instantaneous values of the system clock itself at sample intervals. The timestamps that indicate the presentation time of video and audio are called Presentation Timestamps (PTS). Timestamps that indicate the decoding time are called Decoding Timestamps (DTS). Those timestamps that indicate the value of the system clock are called Program Clock Reference (PCR) in transport streams.
Accordingly, what is needed is a process to analyze video timing information at the head end and down stream (IPTV content distribution site as in FIG. 1), and correlate information from the head end to the down stream video sample instance. The present invention fulfills these needs and provides other related advantages.